- Concomitant Therapy Restrictions: Patients must not be receiving any other anti-cancer agents or radiotherapy at the time of study entry or while on study. Enzyme-inducing anticonvulsants (phenobarbital, phenytoin, carbamazepine) must not be used as these may interfere with irinotecan metabolism. Non-enzyme inducing anticonvulsants (Keppra, etc.) can be used after discussion with study chair. The use of high dose dexamethasone and the use of aprepitant as antiemetics is not recommended due to effects on irinotecan metabolism.